Olefin-based crosslinked thermoplastic elastomers and a process of preparation thereof

ABSTRACT

There is provided olefin-based cross-linked thermoplastic elastomers and a preparation method thereof. The TPE comprises a thermoplastic polyolefin resin; an ethylene-propylene-dien rubber; an ethylene-octene copolymer; and a phenolic cross-linking agent. The TPE shows good tensile strength, tension set and compression set.

This application claims the benefit under 35 USC 371 of prior PCTInternational Application No. PCT/KR97/00114 which has an Internationalfiling date of Jun. 14, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to olefin-based crosslinkedthermoplastic elastomers and a process of preparation thereof. Moreparticularly, the present invention relates to olefin-based crosslinkedthermoplastic elastomers made from an olefin-based resin, anethylene-propylene-diene rubber and an ethylene-octene copolymer andhaving improved properties, and to a process of preparation thereof.

2. Description of the Related Arts

Olefin-based thermoplastic resins modified with elastomers such asrubbers to impart elasticity, or elastomers modified with thermoplasticresins to render having processability are extensively developed due totheir good physical properties and good processability. These types ofmaterials are designated as thermoplastic elastomers because theyexhibit thermoplasticity as well as elasticity. They are advantageous inthat they can be directly molded by using extrusion, injection and pressmolding process without crosslinking-aging step, which is required forcommon rubber to be molded. For this reason, they replace a wide rangeof rubbers needing processability and thermoplastic resins needingelasticity. In particular, olefin-based crosslinked thermoplasticelastomers, unlike styrene-based copolymers or urethane-basedthermoplastic elastomers, show a wide range of physical and processingcharacteristics depending on the degree of crosslinking of elastomersincorporated therein. This renders them applicable to a wide range ofuses and have highest market share. Various researches have been made todevelop new crosslinking systems which can be advantageously used forolefin-based crosslinked elastomers having a same composition. ingeneral, crosslinked thermoplastic elastomers are classified into threegroups: no cured thermoplastic elastomer (hereinafter referred to asTPO) wherein rubbers are incorporated without a crosslinking agent;partially crosslinked thermoplastic elastomers (hereinafter referred toas TPR) wherein rubbers are partially crosslinked into the thermoplasticresin; and completely crosslinked thermoplastic elastomers (hereinafterreferred to as TPV) wherein rubbers are completely crosslinked into thethermoplastic resin.

The degree of crosslinking affects the size and fine dispersion ofrubber particles in crosslinked thermoplastic elastomers, consequentlyaffects elastic characteristics such as tensile strength, permanenttension set, permanent compression set and et al. In more detail, incases of TPO having no crosslinking of rubber and TPR, there arelimitations in obtaining the finely dispersed rubber particles by shearstress. Especially, this becomes more severe as the amount of rubberincreases. For this reason, materials requiring elasticity andthermoplasticity should have been made by the dynamic vulcanization inwhich cured rubbers are pulverized by shear stress during the mixing.

Many developments have been made for crosslinked thermoplasticelastomers. For example, commercial olefin-based crosslinked TPE mayinclude TPR™ by UniRoyal, USA (U.S. Pat. No. 3,758,643), which is thefirst commercial product, and Santoprene™ by Monsanto, USA (U.S. Pat.No. 4,311,628). As crosslinked thermoplastic elastomers using peroxidesas a crosslinking agent, Milastomer™ by Mitsui Petrochemical, Japan(U.S. Pat. No. 4,785,045).

TPR™ and Milastomer™ are crosslinked hermoplastic elastomers in which acombination of polyolefin resin and ethylene-propylene rubber(hereinafter referred to as EPR), or of ethylene-propylene-diene rubber(hereinafter referred to as EPDM) is partially crosslinked by usingperoxide crosslinking agents. When peroxide crosslinking agents are usedfor the crosslinking of rubbers, crosslinking rate and reactivity aregood. On the other hand, peroxide crosslinking agents can not be used ina sufficient amount, since polyolefin is decomposed by the crosslinkingagents. Therefore, there is a limitation in improving the elasticcharacteristics such as permanent compression set or permanent tensionset. Moreover, because the decomposition of polyolefin resin is inducedduring the crosslinking of rubbers goes on, mechanical properties andstability of system are deteriorated.

Santoprene™ is a crosslinked thermoplastic elastomer by completelycrosslinking a combination of polyolefin and EPDM using a phenoliccrosslinking agent. Since a tin-based crosslinking accelerator is usedto increase the rate of crosslinking, the final product has odor andbrownish color, and is apt to absorb moisture. Although the degree ofcrosslinking can be increased since only EPDM rubber is used, theremaining crosslinking agent may cause a excessive crosslinking duringmolding process, consequently the mechanical properties such as tensilestrength and elongation, and permanent compression set are decreased.

Accordingly, olefin-based crosslinked thermoplastic elastomers free fromthe problems of the conventional TPE has been needed.

SUMMARY OF THE INVENTION

Thus, the present invention provides olefin-based crosslinkedthermoplastic elastomers having good elasticity.

The present invention also provides a new crosslinking agent system.

The present invention still provides olefin-based crosslinkedthermoplastic elastomers having good tensile strength and good elasticproperties such as permanent compression set and permanent tension set.

Further, the present invention provides a method for preparingolefin-based crosslinked thermoplastic elastomers.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the findings that partiallycrosslinked thermoplastic elastomers can show better tensile strengthand good elastic properties such as permanent compression set andpermanent tension set than those of completely crosslinked thermoplasticelastomers, when the smaller size and finer dispersion of the rubberparticles in the system is obtained from the reduction of the differenceof interfacial tension and the increase of interfacial adhesion betweenthe components in a multi-component system at the early stage of dynamicvulcanization process.

Thus, a mixture of a conventional polypropylene thermoplastic resin(First component) and ethylene-propylene-diene rubber (Second component)is combined with ethylene-octene copolymer (Third component) to improveinterfacial adhesions, which consequently renders a production ofolefin-based crosslinked thermoplastic elastomers having goodproperties. Ethylene of the third component is the same as ethylene ofthe second component.

According to the present invention, the partially crosslinked thirdcomponent can be obtained by using a proper crosslinking agent system.By using the crosslinking agent system according to the presentinvention, the degree of crosslinking and consequently the density ofcrosslinking can be improved. Thus, it can be crosslinked thermoplasticelastomers showing improved tensile strength and good elastic propertiessuch as permanent compression set and permanent tension set.

The olefin-based crosslinked thermoplastic elastomer (hereinafterreferred to as `TPE`) comprises an olefin-based thermoplastic resin andan olefin-based rubber, and further comprises ethylene-octene copolymerwherein ethylene units are copolymerized with octene in the presence ofa metallocene catalyst.

The TPE according to the present invention comprises, based on 100 partsby weight of following (A)+(B)+(C),

(A) 17-82 parts by weight of a thermoplastic polyolefin resin;

(B) 14.2-76 parts by weight of an ethylene-propylene-diene rubbersatisfying the following conditions;

(a) propylene content: 10-50 wt %

(b) Mooney viscosity at 100° C.: 20-100 ML₁₊₄

(C) 3.8-76 parts by weight of an ethylene-octene copolymer in whichethylene units are copolymerized with octene in the presence ofmetallocene catalyst and which satisfies the following conditions;

(a) octene content: 9.5-30 wt %

(b) melt index: 0.3-30 dg/min.; and

(D) 1-15 parts by weight of a phenolic crosslinking agent.

Each component of the elastomer will be described in detail below.

As a thermoplastic polyolefin resin (A), homopolypropylene or, block orrandom copolymers of ethylene and propylene may be used. When the amountof the resin (A) is less than 17 parts by weight with respect to 100parts by weight of the total amount of (A), (B) and (C), the mechanicalstrength and processability of the resulting TPE are deteriorated. Onthe other hand, when the amount of the resin (A) exceeds 82 parts byweight, impact strength and elasticity of the resulting elastomer aredeteriorated. Therefore, according to the present invention, thepolyolefin resin (A) is used in an amount of 17-82 parts by weight,preferably 20-70 parts by weight based on 100 parts by weight of(A)+(B)+(C).

Ethylene-propylene-diene rubber (`EPDM`) (B) of the present inventionhas been incorporated into crosslinked thermoplastic elastomer asfrequently as ethylene-propylene rubber, since EPDM (B) exhibits goodcompatibility with the resin (A), and better ozone-proof andweatherability than other rubbers such as natural, styrene-butadiene,chloroprene and nitrile-based rubbers. Further, EPDM is advantageousthat it can be crosslinked by phenolic crosslinking agents, since it hasunsaturated bonds between carbon atoms.

For the present invention, 14.2-76 parts by weight, preferably 30-60parts by weight, based on 100 parts by weight of (A)+(B)+(C), of EPDM isused and EPDM has a propylene content of 10-50 wt % and Mooney viscosityat 100° C. of 20-100 ML₁₊₄. When the Mooney viscosity at 100° C. is lessthan 20 ML₁₊₄, mechanical strength of the resulting TPE is deterioratedand dispersive rearrangement by shear stress is not satisfactory. On theother hand, when the Mooney viscosity at 100° C. exceeds 100 ML₁₊₄, theprocessability of the TPE is deteriorated.

Ethylene-octene copolymer (`EOR`) (C) is an ethylene-based rubber inwhich octene is copolymerized as a long branch chain, and is used toincrease elasticity of the TPE due to the increased interfacial adhesionof the system. EOR (C) has an octene content of 9.5-30 wt %. Since EORhaving the octene content more than 10 wt % cannot be obtained by usingZiegler-Natta catalyst, EOR prepared by using metallocene catalyst isused. The preparation of EOR having the octene content of 9.5-30 wt %using metallocene catalyst is described in, for example U.S. Pat. No.5,272,236 and U.S. Pat. No. 5,278,272.

EOR (C) shows good compatibility with EPDM (B) due to ethylenecomponent, and has a narrow molecular weight distribution and uniformphysical properties. Further, EOR (C) exhibits greater heat-resistanceand photo-resistance than other rubbers, due to the presence of octeneunit. Thus, a long branch chain with the octene component imparts glossand clearness to the TPE, and contributes good processability to theTPE. For the present invention, EOR (C) is used in the amount of 3.8-76parts by weight, preferably 20-50 parts by weight based on 100 parts byweight of (A)+(B)+(C). When the amount of EOR (C) exceeds 76 parts byweight, the density of crosslinking is reduced and consequentlyelasticity of the TPE is decreased.

According to the present invention, a phenolic resin is used as acrosslinking agent. In particular, dimethylol phenolic resins mayadvantageously be used. The phenolic resin proceeds with crosslinkingprocess by decomposing unsaturated carbon bonds in EPDM (B), and can beused to sufficient amount since it does not decompose polyolefin resin(A), unlike peroxide crosslinking agent. This enables the degree ofcrosslinking as wide as from 10% to 95%. For the present invention,phenolic resin (D) is used in the amount of 1-15 parts by weight,preferably 3-15 parts by weight based on 100 parts by weight of(A)+(B)+(C). When the amount of phenolic resin (D) exceeds 15 parts byweight, the remaining crosslinking agent (D) after the crosslinkingprocess will proceed with further crosslinking during the subsequentmolding process, eventually resulting in a deterioration of physicalproperties of the molded articles.

According to the present invention, a crosslinking accelerator may beused to increase the rate of crosslinking. The crosslinking accelerator,which may be used for the present invention, may include oxides of Mg,Pb or Zn, in single or combinations thereof. The crosslinkingaccelerator may be used in the amount of 1-7 parts by weight based on100 parts by weight of (A)+(B)+(C).

The crosslinking agent system according to the invention, which iscomprised of a phenolic resin (D) and a metal oxide, can induce acrosslinking of EOR so that it can effectively improve the degree ofcrosslinking compared when only phenolic resin (D) is used. Further, itcan block an excessive crosslinking during the molding process tomaintain the mechanical properties of the TPE stably.

The TPE may be further incorporated with additives which are commonlyused in the resin composition to improve the physical properties of theTPE. The additives may include, but not limited thereto, inorganicadditives such as silica, clay, talc, titanium oxide, zinc oxide or leadoxide, carbon black, flame retardants, thermostabilizers and the like.

The TPE according to the present invention may be prepared by subjectingthe composition containing the components described above to dynamicvulcanization process at a temperature of 170-220° C., 30-120 rpm duringthe retention time of 5-20 minutes.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be described in more detail by way of thefollowing Examples, which should not be considered to limit the scope ofthe present invention.

EXAMPLE 1

40 parts by weight of polypropylene(isotactic index: 98%, melt index: 10dg/min), 50 parts by weight of EPDM(l)(propylene content: 43%, Mooneyviscosity: 65 ML₁₊₄ (100° C.)), 10 parts by weight of EOR(l)(octenecontent: 24%, melt index: 1 dg/min), 1 parts by weight of dimethylolphenolic resin, 1 parts by weight of crosslinking accelerator A(oxidesof Mg), 7 parts by weight of organic additives and proper quantity ofother additives such as antioxidant, antistatic agent andthermostabilizer were mixed in a plasti-corder (mixer for intensivemixing), and dynamic vulcanization process was performed under acondition of 200° C. and 100 rpm, during the retention time of 5minutes. Then, the mixture was dried in an oven of 120° C. for about 2hours. Test specimens were prepared from injection molding.

In order to evaluate the properties of the resulting crosslinked TPE,mechanical properties(stress-strain) was measured according to themethod of ASTM D-412 and D-624, surface hardness was according to themethod of D-2240, permanent compression set was according to the methodof D-395. These methods have been applied for the conventionalcrosslinked thermoplastic elastomers. Further, to measure the degree ofcrosslinking, test specimen was pulverized and then 30 g of the powderwas placed in a boiling xylene for 12 hours. The degree of crosslinkingwas defined as weight of the remaining samples. The results are shown inTable 1.

EXAMPLES 2˜12

By following the procedure of Example 1, crosslinked thermoplasticelastomers were prepared, except that the amount of crosslinking agent,and kind and amount of crosslinking accelerator are selected as shown inTable 1. The properties of the products were measured by the samecriteria and methods in Example 1, and the results are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                      Examples                                                    Components        1  2  3  4  5  6  7  8  9  10 11 12                         __________________________________________________________________________      EPDM(1) 50 50 50 50 50 50 50 50 50 50 50 50                                   EOR(1) 10 10 10 10 10 10 10 10 10 10 10 10                                    Polypropylene 40 40 40 40 40 40 40 40 40 40 40 40                             Crosslinking agent 1 1 1 3 3 3 5 5 5 5 7 7                                    Crosslinking accelerator A 1 --  -- -- 2 2 -- 3 2 2 3 --                      Crosslinking accelerator B -- 1 -- -- 1 -- -- -- 1 -- -- 2                    Crosslinking accelerator C -- -- 1 -- -- 1 -- -- -- 1 -- 1                  __________________________________________________________________________    Properties                                                                          ASTM                                                                              Units                                                                             Temp.                                                           __________________________________________________________________________      Hardness D2240 shore 25° C. 75A 72A 75A 78A 80A 81A 80A 83A 83A                                                         85A 83A 84A                  Tensile D412 kgf/cm.sup.2 25° C. 67 63 69 71 75 77 85 90 90 93                                                          91 94                        strength                                                                      100% D412 kgf/cm.sup.2 25° C. 61 59 60 63 66 68 72 76 78 78 78                                                          79                           Modulus                                                                       Elongation D412 % 25° C. 500 500 500 480 450 430 400 370 380 360                                                        320 300                      Crosslinking Xylene wt % Boil 25 20 21 35 40 43 53 60 61 63 62 63                                                               degree                    __________________________________________________________________________

(Note)

(a) EPDM(1): ethylene-propylene-diene rubber

propylene content: 43%; Mooney viscosity: 65 ML₁₊₄ (100° C.)

(b) EOR(1): ethylene-octene copolymer

octene content: 24%; melt index: 1 dg/min

(c) Polypropylene: manufactured by Honam Petrochemical Corp.

melt index: 10 dg/min; isotactic index: 98%

(d) Crosslinking agent: Dimethylol phenolic resin

(e) Crosslinking accelerator A: Oxides of Mg

(f) Crosslinking accelerator B: Oxides of Pb

(g) Crosslinking accelerator C: Oxides of Zn

EXAMPLES 13˜24

By following the procedure of Example 1, crosslinked thermoplasticelastomers were prepared, except that the amounts of polypropylene,EPDM, EOR and the crosslinking agent, and kind and amount ofcrosslinking accelerator are selected as shown in Table 2. Theproperties of the products were measured by the same criteria andmethods in Example 1, and the results are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                      Examples                                                    Components        13 14 15 16 17 18 19 20 21 22 23 24                         __________________________________________________________________________      EPDM(1) 60 60 60 60 60 60 60 60 60 60 60 60                                   EOR(1) 12 12 12 12 12 12 12 12 12 12 12 12                                    Polypropylene 28 28 28 28 28 28 28 28 28 28 28 28                             Crosslinking agent 5 5 5 5 7 7 7 7 9 9 12 15                                  Crosslinking accelerator A --  3 -- -- -- 4 4 5 7 7 5 --                      Crosslinking accelerator B -- -- 3 -- -- 1 -- -- 3 -- 5 5                     Crosslinking accelerator C -- -- -- 3 -- -- 1 -- -- 3 -- 5                  __________________________________________________________________________    Properties                                                                          ASTM                                                                              Units                                                                             Temp.                                                           __________________________________________________________________________      Hardness D2240 shore 25° C. 62A 64A 64A 64A 64A 66A 68A 66A 68A                                                         68A 68A 70A                  Tensile D412 kgf/cm.sup.2 25° C. 42 48 48 49 49 57 58 55 62 65                                                          66 68                        strength                                                                      100% D412 kgf/cm.sup.2 25° C. 30 38 35 37 35 41 44 39 44 46 46                                                          47                           Modulus                                                                       Elongation D412 % 25° C. 500 450 450 450 410 380 360 400 340 300                                                        280 220                      Permanent D412 % 25° C. 18 15 16 15 15 14 13 14 12 11 10 10                                                              tension set                 Permanent D395 % 70° C. 39 34 35 33 34 30 29 32 30 28 28 27                                                              compression                 set                                                                           Crosslinking Xylene wt % Boil 34 43 40 44 50 57 59 55 72 74 74 75                                                               degree                    __________________________________________________________________________

(Note)

(a) EPDM(1): ethylene-propylene-diene rubber

propylene content: 43%; Mooney viscosity: 65 ML₁₊₄ (100° C.)

(b) EOR(1): ethylene-octene copolymer

octene content: 24%; melt index: 1 dg/min

(c) Polypropylene: manufactured by Honam Petrochemical Corp.

melt index 10 dg/min; isotactic index: 98%

(d) Crosslinking agent: Dimethylol phenolic resin

(e) Crosslinking accelerator A: Oxides of Mg

(f) Crosslinking accelerator B: Oxides of Pb

(g) Crosslinking accelerator C: Oxides of Zn

As shown in Tables 1 and 2, the present invention can providecrosslinked thermoplastic elastomers having various hardnesses andtherein good properties. Also, the degree of crosslinking can beincreased by using phenolic resin together with crosslinking acceleratorof metal oxides, and in these cases the products have prefer propertiesto the product prepared by using only phenolic resin. Further, among thecrosslinking agent systems, system consisting of phenolic resin, oxidesof Mg and oxides of Zn is the most effective.

EXAMPLES 25˜32 AND COMPARATIVE EXAMPLES 1˜2

By following the procedure of Example 1, crosslinked thermoplasticelastomers were prepared, except that the amounts of polypropylene andthe crosslinking agent, and kinds and amounts of EPDM, EOR andcrosslinking accelerator are selected as shown in Table 3. Theproperties of the products were measured by the same criteria andmethods in Example 1, and the results are shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                      Comp.                        Comp.                            Example Example Example                                                     Components        1    25 26 27 28 29 30 31 32 2                              __________________________________________________________________________      EPDM(2) 76 56 56 56 66 46 36 26 16 --                                         EOR(2) -- 20 -- -- -- -- -- -- -- --                                          EOR(3) -- -- 20 -- 10 30 40 50 60 76                                          EOR(4) -- -- -- 20 -- -- -- -- -- --                                          Polypropylene 24 24 24 24 24 24 24 24 24 24                                   Crosslinking agent 12 12 12 12 12 12 12 12 12 12                              Crosslinking accelerator A  4 4 4 4 4 4 4 4 4  4                              Crosslinking accelerator B  2 2 2 2 2 2 2 2 2  2                            __________________________________________________________________________    Properties                                                                          ASTM                                                                              Units                                                                             Temp.                                                           __________________________________________________________________________      Hardness D2240 shore 25° C. 63A 66A 66A 66A 64A 70A 85A 40D 50D                                                     60D                              Tensile D412 kgf/cm.sup.2 25° C. 55 58 65 70 60 71 62 48 55 65                                                       strength                        100% D12 kgf/cm.sup.2 25° C. 41 47 56 59 52 59 47 25 30 31                                                           Modulus                         Permanent D412 % 25° C. 12 10 9 9 11 8 12 25 -- --                     tension set                                                                   Permanent D395 % 70° C. 28 25 23 23 25 23 27 35 -- --                  compression                                                                   set                                                                           Crosslinking Xylene wt % Boil 83 68 71 70 75 61 49 44 30 12                   degree                                                                      __________________________________________________________________________

(Note)

(a) EPDM(2): ethylene-propylene-diene rubber

propylene content: 35%; Mooney viscosity 69 ML₁₊₄ (100° C.)

(b) EOR(2): ethylene-octene copolymer

octene content: 30%; melt index: 0.3 dg/min

(c) EOR(3): ethylene-octene copolymer

octene content: 20%; melt index: 18 dg/min

(d) EOR(4): ethylene-octene copolymer

octene content: 9.5%; melt index: 30 dg/min

(e) Polypropylene: manufactured by Honam Petrochemical Corp.

melt index: 10 dg/min; isotactic index: 98%

(f) Crosslinking agent: Dimethylol phenolic resin

(g) Crosslinking accelerator A: Oxides of Mg

(h) Crosslinking accelerator B: Oxides of Pb

The results of Table 3 show that apart from EPDM, some amount of EOR mayalso be crosslinked by using the crosslinking agent system according tothe present. That is to say, the crosslinking system with metal oxidesmay induce the crosslinking reaction of EOR, and thereby the degree ofcrosslinking can be increased. This shows that, within the same amountof rubber, the crosslinked thermoplastic elastomers prepared by usingEOR together with EPDM have better properties than those prepared byusing only EPDM. But, the crosslinked thermoplastic elastomer preparedby using only EOR(the product of Comp. Example 2) has poor propertiesdue to the low degree of crosslinking.

EXAMPLES 33˜43

Examples 33˜43 are provided for illustrating the properties of thecrosslinked thermoplastic elastomers prepared by varying the kind ofEPDM.

By following the procedure of Example 1, crosslinked thermoplasticelastomers were prepared, except that the amounts of polypropylene, EOR,the crosslinking agent and the crosslinking accelerator, and kind andamount of EPDM are selected as shown in Table 4. The properties of theproducts were measured by the same criteria and methods in Example 1 andthe results are shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                      Examples                                                    Components        33 34 35 36 37 38 39 40 41 42 43                            __________________________________________________________________________      EPDM(3) 65.6 60 --  --  --  51.3 42.7 34 26.1 17.4 14.2                       EPDM(4) -- -- 60 -- -- -- -- -- -- -- --                                      EPDM(5) -- -- -- 60 -- -- -- -- -- -- --                                      EPDM(6) -- -- -- -- 60 -- -- -- -- -- --                                      EOR(1) 17.4 16 16 16 16 13.7 11.3 9 6.9 4.6 3.8                               Polypropylene 17 24 24 24 24 35 46 57 68 78 82                                Crosslinking agent 7.6 7 7 7 7 6 5 4 3 2 1.7                                  Crosslinking accelerator A 5.5 5 5 5 5 4.3 3.6 2.8 2.2 1.5 1.2              __________________________________________________________________________    Properties                                                                          ASTM                                                                              Units                                                                             Temp.                                                           __________________________________________________________________________      Hardness D2240 shore 25° C. 56A 64A 62A 62A 60A 70A 78A 86A 43D                                                      50D 55D                         Tensile D412 kgf/cm.sup.2 25° C. 46 55 53 53 50 70 78 110 180                                                        230 260                         strength                                                                      100% D412 kgf/cm.sup.2 25° C. 37 42 40 40 36 47 53 85 120 160                                                        180                             Modulus                                                                       Elongation D412 % 25° C. 220 270 300 300 320 320 330 420 530 580                                                     600                             Permanent D412 % 25° c. 8 12 13 13 14 13 16 23 42 48 --                tension set                                                                   Permanent D395 % 70° C. 25 29 30 30 32 30 32 38 45 -- --                                                              compression                    set                                                                           Crosslinking Xylene wt % Boil 79 73 69 68 65 64 55 46 39 30 27                degree                                                                      __________________________________________________________________________

(Note)

(a) EPDM(3): ethylene-propylene-diene rubber

propylene content: 15%; Mooney viscosity: 72 ML₁₊₄ (100° C.)

(b) EPDM(4): ethylene-propylene-diene rubber

propylene content: 25%; Mooney viscosity: 50 ML₁₊₄ (100° C.)

(c) EPDM(5): ethylene-propylene-diene rubber

propylene content: 37%; Mooney viscosity: 20 ML₁₊₄ (100° C.)

(d) EPDM(6): ethylene-propylene-diene rubber

propylene content: 46%; Mooney viscosity: 100 ML₁₊₄ (100° C.)

(e) EOR(1): ethylene-octene copolymer

octene content: 24%; melt index: 1 dg/min

(f) Polypropylene: manufactured by Honam Petrochemical Corp.

melt index: 10 dg/min; isotactic index: 98%

(g) Crosslinking agent: Dimethylol phenolic resin

(e) Crosslinking accelerator A: Oxides of Mg

EXAMPLES 44˜46 AND COMPARATIVE EXAMPLES 3˜11

By following the procedure of Example 1, crosslinked thermoplastic 10elastomers were prepared, except that the amounts of polypropylene andthe crosslinking agent, and kinds and amounts of EPDM, EOR andcrosslinking accelerator are selected as shown in Table 5. Theproperties of the products were measured by the same criteria andmethods in Example 1, and the results are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________                      C. Ex.                                                                            Ex.                                                                              C. Ex.   Ex.                                                                              C. Ex.   Ex.                                                                              C. Ex.                       Components        3   44 4  5  6  45 7  8  9  46 10 11                        __________________________________________________________________________      EPDM(4) 76 56 56 56 59 39 39 39 42 30 30 30                                   EOR(5) --  20 -- 10 -- 20 -- 10 -- 12 -- 6                                    Styrene-butadien rubber -- -- 20 10 -- -- 20 10 -- -- 12 6                    Polypropylene 24 24 24 24 41 41 41 41 58 58 58 58                             Crosslinking agent 9 9 9 9 7 7 7 7 5 5 5 5                                    Crosslinking accelerator A 3 3 3 3 4 4 4 4 4 4 4 4                            Crosslinking accelerator B 2 2 2 2 2 2 2 2 1 1 1 1                          __________________________________________________________________________    Properties                                                                          ASTM                                                                              Units                                                                             Temp.                                                           __________________________________________________________________________      Hardness D2240 shore 25° C. 65A 66A 64A 65A 73A 75A 72A 73A 82A                                                          84A 81A 82A                 Tensile D412 kgf/cm.sup.2 25° C. 53 56 48 48 74 79 68 70 87 91                                                           83 85                       strength                                                                      100% D412 kgf/cm.sup.2 25° C. 40 44 35 36 50 55 46 50 58 62 50                                                           54                          Modulus                                                                       Permanent D412 % 25° C. 13 11 14 14 15 14 17 16 17 15 18 18                                                               tension set                Permanent D395 % 70° C. 29 27 31 32 32 30 34 33 34 32 36 35                                                               compression                set                                                                           Crosslinking Xylene wt % Boil 83 72 62 66 65 55 46 50 49 44 36 41                                                                degree                   __________________________________________________________________________

(Note)

(a) EPDM(4): ethylene-propylene-diene rubber

propylene content: 25%; Mooney viscosity: 50 ML₁₊₄ (100° C.)

(b) EOR(5): ethylene-octene copolymer

octene content: 19%; melt index: 30 dg/min

(c) Styrene-butadiene rubber: styrene content: 23%

(d) Polypropylene: manufactured by Honam Petrochemical Corp.

melt index: 10 dg/min; isotactic index: 98%

(e) Crosslinking agent: Dimethylol phenolic resin

(f) Crosslinking accelerator A: Oxides of Mg

(g) Crosslinking accelerator B: Oxides of Pb

As shown in Table 5, the crosslinked thermoplastic elastomers preparedby using styrene-butadien rubber(SBR) together with EPDM have inferiorproperties to the products prepared by using only EPDM or using EOR andEPDM. This indicates that SBR is not crosslinked by the crosslinkingagent system according to the present, and that the interfacialadhesions between SBR and EPDM or polypropylene are weak.

As above described, according to the present invention, ethylene-octenecopolymer incorporated in the crosslinking system comprisingolefin-based thermoplastic resin and olefin-based rubber may bepartially crosslinked by the crosslinking agent system consisting ofphenolic resin and metal oxides and exist in the form of fine anduniform dispersion. Further, the interfacial adhesion between theethylene-octene copolymer and the crosslinked ethylene-propylene-dienrubber can increase the degree of crosslinking. Consequently, thecrosslinked thermoplastic elastomers provided by the present inventionhave good properties such as the tensile strength, tension set,compression set and the like.

Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the art will stillfall within the spirit and scope of the present invention as defined inthe appended claims.

What is claimed is:
 1. An olefin-based crosslinked thermoplasticelastomer comprising, based on 100 parts by weight of following(A)+(B)+(C),(A) 17-82 parts by weight of a thermoplastic polyolefinresin; (B) 14.2-76 parts by weight of an ethylene-propylene-diene rubberwhich satisfies the following conditions;(a) propylene content: 10-50 wt% (b) Mooney viscosity at 100° C.: 20-100 ML₁₊₄ (C) 3.8-76 parts byweight of an ethylene-octene copolymer which satisfies the followingconditions;(a) octene content: 9.5-30 wt % (b) melt index: 0.3-30dg/min.; and (D) 1-15 parts by weight of a phenolic crosslinking agent.2. The olefin-based crosslinked thermoplastic elastomer according toclaim 1, which comprises, based on 100 parts by weight of following(A)+(B)+(C),(A) 20-70 parts by weight of a thermoplastic polyolefinresin; (B) 30-60 parts by weight of an ethylene-propylene-diene rubberwhich satisfies the following conditions;(a) propylene content: 10-50 wt% (b) Mooney viscosity at 100° C.: 20-100 ML₁₊₄ (C) 20-50 parts byweight of an ethylene-octene copolymer which satisfies the followingconditions;(a) octene content: 9.5-30 wt % (b) melt index: 0.3-30dg/min.; and (D) 3-15 parts by weight of a phenolic crosslinking agent.3. The olefin-based crosslinked thermoplastic elastomer according toclaim 1 or 2, wherein said ethylene-octene copolymer is obtained bycopolymerizing ethylene units with octene in the presence of metallocenecatalyst.
 4. The olefin-based crosslinked thermoplastic elastomeraccording to claim 1 or 2, wherein said polyolefin thermoplasticresin(A) is homopolypropylene or, lock or random copolymers of ethyleneand propylene.
 5. The olefin-based crosslinked thermoplastic elastomeraccording to claim 1 or 2, wherein said the phenolic crosslinking agentis dimethylol phenolic resins.
 6. The olefin-based crosslinkedthermoplastic elastomer according to claim 1 or 2, which furthercomprises one or more crosslinking accelerators selected from a groupconsisting of oxides of Mg, Pb and Zn in an amount of 1-7 parts byweight based on 100 parts by weight of (A)+(B)+(C).
 7. A method forpreparing an olefin-based crosslinked thermoplastic elastomer, whichcomprises step of dynamical vulcanization following components (A)-(D)at a temperature of 170-220° C., 30-120 rpm during retention time of5-20 minutes,(A) 17-82 parts by weight of a thermoplastic polyolefinresin; (B) 14.2-76 parts by weight of an ethylene-propylene-diene rubberwhich satisfies the following conditions;(a) propylene content: 10-50 wt% (b) Mooney viscosity at 100° C.: 20-100 ML₁₊₄ (C) 3.8-76 parts byweight of an ethylene-octene copolymer which satisfies the followingconditions;(a) octene content: 9.5-30 wt % (b) melt index: 0.3-30dg/min.; and (D) 1-15 parts by weight of a phenolic crosslinking agent,wherein said parts by weight being based on 100 parts by weight of(A)+(B)+(C).
 8. The method according to claim 7, wherein saidethylene-octene copolymer is obtained by copolymerizing ethylene unitswith octene in the presence of metallocene catalyst.
 9. The methodaccording to claim 7, wherein one or more crosslinking acceleratorsselected from a group consisting of oxides of Mg, Pb and Zn in an amountof 1-7 parts by weight based on 100 parts by weight of (A)+(B)+(C) areincorporated.